Effect of binary cement replacement materials on sulfuric acid resistance of dense concretes

Biogenic sulfuric acid corrosion is often a problem in sewer environments. Also in certain industrial activities sulfuric acid is used during the production process. It can lead to a fast degradation of the concrete structures. There is therefore a substantial need for construction of durable concrete structures in such environments. The porosity of concretes plays an important role in harsh environments. For production of low-porosity concretes, optimisation of aggregate and cement grading and their proportions is necessary. A research programme was conducted to investigate concrete resistance in a sulfuric acid environment. Four concrete groups were investigated. The first group contains type II Portland cement as a control mix and the second group contains cement and superfine quartz powder as a filler with particle size less than 16 mu m. The third group includes three different mixtures containing cement and cement material replacements including 8% silica fume, 20% trass and pumice as natural pozzolans and a super-fine filler. Finally three mixtures were designed in the last group based on binary cement replacement materials containing cement with 15% natural pozzolans and 8% silica fume or 10% trass and 10% pumice and super-fine filler. The dense packing of siliceous aggregates and cementitious materials was used to achieve the highest density of concretes. Cementitious material content and water-binder (w/b) ratio were varied in this investigation. In the experiment, specimens were immersed in sulfuric acid with pH = 1.0. They were periodically examined for appearance, measured for mass change and tested in compression and flexure up to 180 days. Results show that the mass loss of mortar specimens immersed in sulfuric acid solutions increased as the w/b ratio decreased. There is, however, an optimum cementitious material content for each mixture. The performance of mortar and concretes containing trass and ultra-fine filler was better than the other mixes. Contradictory results were obtained for the concretes containing silica fume in sulfuric acid environments.